1. Field of the Invention
This invention relates to a head box for flowing a paper material slurry on to a paper forming endless belt in a paper machine.
2. Prior Art
A head box (stock inlet) is located in the very beginning of a wet part in a paper machine. This place becomes one of the most important parts for deciding the texture of paper, etc.
In keeping with the increased paper manufacturing speed and the enlarged paper forming width, the conventional evener roll type inlet was disappeared and a high turbulence head box came to the mainstream.
With regard to the above, various makers adopt their own design. The important part of the construction is that a defuser, which has a numerous paper material slurry flowing pores, is disposed on an inlet side of a paper material passage leading to a slice lip to form a dispersing section, the flowing speed of the paper material slurry flowing through the dispersing section is rapidly increased to create turbulence, thereby to enhance the dispersion of the entire fabric in the paper forming width direction so as to improve a profile in the width direction.
One representative example of the above is that the defuser is formed by uniformly arranging pipes having a small diameter and forming the paper material slurry passage in juxtaposed relation in high density.
However, in order to obtain an initial turbulence by the defuser, it is necessary that the absolute length of the paper material slurry flowing pore or pipe is made sufficiently long or the defuser is provided in a multistage because otherwise the improvement of the profile in the paper forming direction cannot be expected. Such defuser invites a large size of the head box and the manufacturing cost becomes high. Also, if the absolute length of the paper material slurry flowing pore becomes longer, the pressure loss due to friction of the inner wall of the flowing pore becomes larger, and therefore the paper material slurry must be fed by a correspondingly high pump. Since this is contrary to energy saving, there is a demand that the profile effect is obtained at the lowest limit of the flowing speed.
More specifically, in order to uniformalize the profile in the entire paper forming direction, the paper material slurry flowing pores are required to be arranged in high density as much as possible with respect to a section in the paper material slurry flowing direction. However, if the pores are arranged in such high density, we would come up against a dilemma that the flowing speed cannot be increased and a lowering of the turbulence effect is invited. Therefore, there is a limit in improving the profile if only by the defuser.